DESCRIPTION (Adapted from the Investigator's Abstract): The investigators will study a relatively genetically homogeneous population to test the hypotheses that genetic factors are linked to bipolar disorder. The study will focus on the population of the Azores, a nine island archipelago in the Atlantic Ocean. The Azores have a centralized health system. All ten psychiatrists on the islands are collaborating with the investigators on this project. The investigators are currently funded to study schizophrenia in this same population and believe that it is critical to study all of the patients suffering with bipolar including over 300 affected family members. The pilot study has already identified 25 families with 84 affected members. A complementary strategy will be used to study candidate loci. They will study a sample of 225 subjects suffering from bipolar disorder and their parents (Total n=675) employing the haplotype relative risk and the transmission/disequilibrium test strategies. This strategy insures that the investigators control for all ancestry for each subject, using the uninherited haplotype derived from the two parents. The third sample will include all other Azorean patients with bipolar disorder in the Azores. This will be a valuable sample for assessing the prevalence of any mutations that are identified in the population. These complementary strategies will allow them to cross validate any positive results. The careful diagnostic definition of phenotype will be based on detailed structured clinical data employing the diagnostic interview for genetic studies (DIGS), which they have translated into Portuguese. The project is designed to capture a very complete history of the patient's illness, as well as to be able to follow most subjects prospectively for a long period of time. This will be extremely valuable for achieving diagnostic certainty, and minimizing false positives. The Whitehead/MIT Center for Genome Research will perform a genome-wide scan and collaborate on all data analysis for the project.